In long term evolution (LTE), the paging procedure is performed by a Node B (NB) to notify a user equipment (UE) about incoming sessions and changes in system information. The UE listens for paging messages addressed to the UE using a periodic search window which is configured by a cell, in which the UE is currently camped. When the UE detects a paging message addressed by the NB, the UE initiates the system access procedure for connection establishment. The NB configures paging occasions (PO) for each UE, at which the NB can transmit physical downlink control channel (PDCCH) message containing the scheduling information of Physical Downlink Shared Channel (PDSCH) message (i.e. paging message) for the UE. Each PDSCH message may consist of paging messages for multiple UEs. Each UE monitors a subset of the system frames and subframes for paging based on following identifiers configured for the UE: UE Identity (UE_ID), TeDRX,H (extended DRX cycle length in hyper frames, if configured), L (length of paging transmission window in seconds, if configured), and T (length of the DRX cycle).
Specifically, if the UE is configured with eDRX mode, the UE monitors hyper-frames known as paging hyper-frames (PH), which satisfies the following relation:H-SFN mod TeDRX,H=(UE_ID mod TeDRX,H),in which UE_ID is UE identity derived from international mobile subscriber identity (IMSI) of UE.
Within the configured PH, a Paging Transmission Window (PTW) is defined. The UE monitors the system frames for paging (based on Paging Frames (PF) calculation) within the PTW. Each PF may consist of a single or multiple POs. Each PO occupies a sub-frame of a particular PF. The starting System Frame Number (SFN) for the PTW is as follows:SFN=256*ieDRX,in which ieDRX=floor(UE_ID/TeDRX,H)mod 4
Within the PTW, the UEs monitor POs within PFs. The PFs are determined as follows:SFN mod T=(T div N)*(UE_ID mod N)
The index is is pointing to a PO from sub-frame pattern is derived as follows:is=floor(UE_ID/N)mod Ns here, nB=4T, 2T, T, T/2, T/4, T/8, T/16, T/32; N=min (T,nB); Ns=max (1,nB/T).
The NB determines the POs which are being monitored by the each UE. The NB transmits the paging message for a particular UE in the POs, which that particular UE is monitoring. The usage of same value of UE_ID for computing of PH and PF results in an uneven distribution of paging load (i.e. number of UEs monitoring a radio resource for paging) across different POs. In an example, within one hyper-frame it is possible that a thousand UEs are monitoring a particular system frame number (SFN), while all the remaining SFNs available for paging are not monitored by any of the UEs. The variation in the distribution of number of UEs monitoring across different POs is more pronounced when the common divisor of TeDRX, H and T is large in number. Since, one of the primary objectives of PO computation is non-varying paging load distribution across radio resources available for paging; the variation of the paging load distribution may lead to performance degradation of the overall system. Specifically, varying paging load distribution may lead to radio resource wastage and increased delay for the UEs.
For coverage enhancement (CE) mode, physical downlink shared channel (PDSCH) and physical downlink control channel (PDCCH) messages, respectively, have to be repeated multiple times to ensure that UEs operating in the CE mode are able to decode the PDCCH and PDSCH reliably. Since, PO configuration for a UE does not utilize the CE Level (CEL) to determine the POs to be monitored by the UE, each PO can be monitored by UEs with different CELs. As the PDSCH may contain paging message for multiple UEs, for reliable decoding, the PDCCH and the PDSCH need to be transmitted at least with a repetition level corresponding to the UE with highest value of CEL, which is to be paged in the given PO. Hence, this leads to unnecessary repetitions for UEs with lower CEL values monitoring the same PO. This may result in excessive power consumption for the UEs with low CEL value, in monitoring redundant PDCCH and PDSCH. It also results in radio resource wastage (and reduced capacity) from network perspective as the UEs with low CEL value need to be paged corresponding to highest repetition level.
Thus, there is a need of having a method which allows uniform distribution of UEs across different POs when configured with eDRX and another method which allows categorizing UEs based on the CEL to monitor PO.
The above information is presented as background only to help the reader for understanding the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.